1. Field of the Invention
This invention relates to a television (TV) signal level meter (electric field strength meter), and more particularly to a meter of this kind for use in measuring and displaying an electric field strength of a radio wave of each television channel included in the VHF/UHF ranges or the like.
2. Prior Art
Conventionally, a TV signal level meter or a spectrum analyzer is used for measuring an electric field strength of a radio wave received in a TV channel. The TV signal level meters may be classified into a single channel type and a multi-channel type. One such single channel type TV meter is a VHF/UHF signal level meter LFC-945 manufactured by the present assignee which is adapted to measure and indicate an electronic field strength level of a selected single channel. On the other hand, one type of multi-channel type TV signal level meter is MODEL NLC-W901 manufactured by Nippon Antenna Co., which simultaneously measures and indicates electric field strength levels of up to a predetermined number of channels (for example seven channels). A spectrum analyzer, though not exclusively employed for the measurement of TV signal levels, can also be used for measuring the electric field strength magnitudes of TV channels since it can display the levels of received signals within a certain frequency range.
Since the above-mentioned single channel type TV signal level meter cannot simultaneously display electric field strength levels of a plurality of channels, it takes a long time to measure the levels of a large number of channels. In condominiums and apartment complexes and so on, it has been required that outputs from an installed common antenna to respective dwelling units must have signal levels not lower than a predetermined value at any channel. In meeting such a requirement, adjustment of the antenna by using a single channel type TV meter requires a great deal of labor. Further, since the number of channels which require measurements of signal levels has been increasing with the recently wide-spread installation of a city-type CATV or the like, the labor for measuring and checking signal levels of these channels becomes immense.
This problem can be alleviated to some extent by the foregoing multi-channel type TV signal level meter MODEL NLC-W901. This TV level meter, however, divides a measurable level range into a high region (60-100 dB.mu.) and a low region (30-70 dB.mu.) and thus has a narrow dynamic range for the simultaneous display of measured results. Specifically, if there is a large difference in level among channels, the measured levels of all channels cannot be displayed at one time. Thus, the TV signal level meter of this model is not suitable for the requirement of the collective residence. The model also suffers a drawback that selection and change of channels to be measured take much time.
If a spectrum analyzer is employed for measuring TV channel signal levels, the levels of all signals present within a certain frequency range are displayed. Due to this, it is inconvenient to find the signals of TV channels to be measured. There is another drawback that the device itself is very expensive.